


r V # S 















» *^ 




















r O 










,v u ^ 



^ t> < ^M^>^^ ** M ,$ 




^ '•« s * A <, *o,** ,g v 



^o 15 



K^ ^ 



? .»i^L'* ^ 




<"" ° '' ^ 




oY 







%/ ■ •* 




.G^ V> *'V;s 4 A <-, -ow 














*bV" 



4 o 

%: /K Ifff!- J\ ijgg) }\ l^.-/\-. _, 

<f..tifcr.\. .c» 4 .-isit>o ./\v^/^ /,^%A >*\.^i:/V 










l V . o » « 






A^*V 



^5 ^ -, 







^^ 



\~ V . r, **"S. A > * • • 










"' ^ 






f :Mk\ \f -i 



<, *^v g* *o '*.»* O <* *<tvT* g* *o, -«.T* A <\ *T^T» .g* X 




» ^ 











^ v 

X *; 




.v O * 









"ot? 









<. 







.o° V**?^ ^ X**° 



IP"** 



^ 




•/ X/^> o 



o, * 








"of 

ip-n^ 



^ S X 
^ X 




°o 

























r »' 



6 V ^ 




-^ -^ 



°o 



A 






jP^ 



c5°^ 






a* 5 *" t ,*Z' *■> v v ,»?-^L% "<^ 









• A V -^ 




^.^ 



* A V -^ : 



^°^ 



^0^ 



*» < 

^0^ 




/Jfe*-. S.J' :Mfc. \^ .•»'•. \/ ;^ 



. . » • «G 




tt A Vy ^ - 














•• **x 




.6- v : — : x^" ^'• : 5W f V V- 



** t^a-X^*^ ^A 









J£J 8913 



Bureau of Mines Information Circular/1983 



A/ ^ 2^1983 



Dolomite Refractories, and Their 
Potential as Substitutes 
for Imported Chromite 



By Timothy A. Clancy 



UNITED STATES DEPARTMENT OF THE INTERIOR 



Information Circular 8913 



Dolomite Refractories, and Their 
Potential as Substitutes 
for Imported Chromite 



By Timothy A. Clancy 




UNITED STATES DEPARTMENT OF THE INTERIOR 
James G. Watt, Secretary 

BUREAU OF MINES 
Robert C. Horton, Director 

Research at the Tuscaloosa Research Center is carried out under a cooperative agreement between the U.S. 
Department of the Interior, Bureau of Mines, and the University of Alabama. 



This publication has been cataloged as follows: 




Clancy, T. A. (Timothy A.) 

Dolomite refractories, and their potential as substitutes for im- 
ported chromite. 

(Bureau of Mines information circular ; 8913) 

Bibliography: p. 17-18. 

Supt. of Docs, no.: I 28.27:8913. 

1. Dolomite. 2. Refractory materials. 3. Chromium ores. I. Ti- 
tle. II. Series: Information circular (United States. Bureau of Mines) ; 
8913. 



TN295.U4 [TN957] 622s [666'. 72] 82-600333 



CONTENTS 



Page 



Abstract 1 

Introduction 1 

Dolomite ore 2 

Origin and mineralogy • 2 

Refractory grade dolomite. 2 

U.S. dolomite deposits. 4 

Dolomite refractories 4 

Aggregate processing 4 

Brick processing 7 

Brick usage 8 

United Kingdom 8 

Europe 8 

Japan 8 

United States 9 

Properties of 14 U.S. dolomites 10 

Materials and test procedures 10 

Results and discussion . . 11 

Summary 15 

References 17 

ILLUSTRATIONS 

1. Photomicrograph of Ohio dolomite No. 1 presently used to produce refractory 

products 13 

2. Photomicrograph of Missouri dolomite presently used to produce refractory 

products 13 

3. Photomicrograph of Alabama dolomite No. 3 14 

4. Photomicrograph of Pennsylvania dolomite No. 3 14 

5. DTA curves for six dolomites.... 16 

6 . DTA curves for five dolomites 16 

7 . DTA curves for three dolomites 16 

8. TGA curve for a sample of Pennsylvania dolomite No. 2 16 

9. TGA curve for a sample of Michigan dolomite No. 1 17 

TABLES 

1 . Mineralogical properties of dolomite 2 

2. Classification of granular refractory dolomite 3 

3. Composition and properties of refractory grade dolomites..... 3 

4 . Typical properties of dead-burned dolomite grains 7 

5. Distribution of steel production by process 9 

6. Approximate distribution of BOF brick usage in the United States 9 

7. Dolomite brick properties 10 

8. Properties of raw domestic dolomites 11 

9. Petrographic analysis data for raw domestic dolomites 12 





LIST OF UNIT OF MEASURE ABBREVIATIONS USED 


IN 


THIS REPORT 


Btu/f t3 


British thermal unit per 
cubic foot 


pm 
mm 




micrometer 
millimeter 


° C 


degree Celsius 


pet 




percent 


g/cm 3 


gram per cubic centimeter 


pct/min 




percent per minute 


hr 


hour 


psi 




pound per square inch 


lb 


pound 


wt-pct 




weight-percent 


tain 


minute 









DOLOMITE REFRACTORIES, AND THEIR POTENTIAL AS SUBSTITUTES 

FOR IMPORTED CHROMITE 

By Timothy A, Clancy 1 



ABSTRACT 

To help reduce the Nation's dependence on imported chromite, the Bu- 
reau of Mines is conducting research on the use of dolomites as an 
alternate material. Dolomite is a plentiful domestic resource and of- 
fers certain advantages as a refractory raw material. A review of the 
literature has indicated that there are many sources of high-purity 
dolomite in this country and that European nations use a greater pro- 
portion of dolomite refractories, primarily in steelmaking, than the 
United States. The Bureau of Mines characterized 14 domestic dolomites 
as to chemistry, density, mineralogy, microstructure, and thermal 
behavior, to develop baseline data on their suitability as refractory 
raw materials. 

INTRODUCTION 

To help ensure a dependable domestic supply of essential minerals, 
the Bureau of Mines initiated an evaluation of domestic dolomites as a 
refractory raw material. Increased use of domestic dolomite as a re- 
fractory material would lessen the Nation's dependence on imported 
chromite and high energy consuming materials, such as seawater peri- 
clase. Historically, (10) 2 the United Kingdom, West Germany, Austria, 
and Japan have developed greater use of dolomite refractories than the 
United States particularly in secondary refining processes for steel- 
making. In 1979, Western Europe used 28.6 lb of dolomite refractories 
per ton of steel produced versus 14.8 lb of dolomite refractories for 
the United States. 

This paper reviews the properties and uses of dolomite refractories. 
Some preliminary data on the chemical and physical properties for 
14 different raw domestic dolomite ores are included. These data will 
be used in future studies for comparison with the refractory properties 
of calcined grain produced from these ores. 

- ■ — 

'Supervisory ceramic engineer, Tuscaloosa Research Center, Bureau of Mines, Univer- 
sity, AL. 

•^Underlined numbers in parentheses refer to items in the list of references at the 
end of this report. 



DOLOMITE ORE 



ORIGIN AND MINERALOGY 

Dolomite (2) (CaC0 3 •MgC0 3 ) , identified 
by Dolomieu in 1791, occurs as sedimen- 
tary deposits similar in nature to lime- 
stone. Geologically some dolomites are 
precipitated directly from seawater but 
most dolomites are a result of the alter- 
ation of calcium carbonate sediments or 
rocks by hypersaline brines. Good exam- 
ples are the almost-pure dolomite Silu- 
rian reefs in northern Illinois, Indiana, 
and Ohio, and in southern Michigan. Oth- 
er carbonate minerals are found associ- 
ated with dolomite, but usually not in 
great quantities. 

Because of their similar physical prop- 
erties, it is not easy to distinguish one 
carbonate mineral from another. The rate 
of solubility of the different minerals 
in dilute hydrochloric acid is the best 
technique to identify them in the field. 
Calcite is much more soluble in dilute 
acid than dolomite, so if a fresh rock 
surface is etched, the amount of dolomite 
left in relief can be estimated visually. 
X-ray diffraction is commonly used in the 
laboratory for determining carbonate min- 
eralogy of bulk samples. Thin section 
petrographic analysis may be helpful, al- 
though it is difficult to distinguish 
carbonates in thin section unless stain- 
ing techniques are used. 

Impurities in dolomites vary consider- 
ably, but are economically important only 
if they affect the end uses of the rock. 
Impurities are tolerable for some uses 
if disseminated uniformly throughout the 
rock. Probably the most common impur- 
ity in dolomites is clay. The clay min- 
erals, mainly kaolinite, illite, chlo- 
rite, smectite, and mixed lattice types, 
may be either evenly distributed or con- 
centrated in laminae or thin partings. 
Chert, another common impurity, may be 



disseminated, or concentrated in nodules, 
lenses, or beds. It is composed mainly 
of very fine quartz (Si02) that easily 
incorporates impurities into its struc- 
ture so it may be found in almost 
all colors. Silica is also found in 
dolomites as discrete silt or sand-size 
grains of quartz. 

Dolomite and other carbonates are nor- 
mally classified as to composition. 
High-calcium limestone is more than 95 
pet CaC03 , high-purity carbonate rock is 
more than 95 pet combined CaC03 and 
MgC03 , and high-magnesium dolomite is 
more than 43 pet MgC03 (theoretically 
pure dolomite is 45.7 pet MgC03). The 
mineralogical properties of dolomite are 
given in table 1. 

TABLE 1. - Mineralogical properties 
of dolomite 

Crystal system Hexagonal. 

Moh's hardness 3.5 to 4.0. 

Specific gravity.... 2.87 

Color White or pink. 

Refractive indices: 

e 1.500 

a) 1.679 

Birefringence, 6.... 0.179 

Solubility Slightly soluble in 

cold dilute HC1 . 

REFRACTORY GRADE DOLOMITE 

The American Society for Testing and 
Materials (1_) classifies dolomite refrac- 
tory raw materials as (1) raw refractory 
dolomite, (2) calcined refractory dolo- 
mite, and (3) dead-burned refractory do- 
lomite. This classification is based 
primarily on MgO content, loss on igni- 
tion, and impurity contents. Table 2 
lists the requirements for each of these 
classes of refractory dolomite. 



TABLE 2. - Classification of granular refractory dolomite 
(ASTM C468-70) , weight-percent 



Classes 



MgO 
content , 
minimum 



Loss on 

ignition, 

maximum 



Impurities, maximum 



SiO- 



A1 2 3 
+ Ti0 2 



Fe 2 3 
range 



Sulfur 



16 
33 

32 



Raw refractory dolomite, 

"as received" basis 

Calcined refractory dolomite, 

ignition-free basis 

Dead-burned refractory dolomite 

(rotary kiln-fired), ignition-free 

basis 

NAp Not applicable. 



The use of dolomite as a refractory ap- 
pears to have started in about 1878 when 
S. G. Thomas experimented with tar-bonded 
dolomite linings in a Bessemer converter. 
Much of present-day dolomite refractory 
technology was developed in England dur- 
ing World War II. Since then, England 
has made great use of dolomite raw mate- 
rials for refractories. Chesters (4), in 
a chapter devoted to dolomite, presents 



NAp 
2.0 

2.0 



1.75 
2.00 

2.25 



1.50 
2.50 

2.50 



NAp 
NAp 

4-10 



0.08 
.16 

NAp 



the compositions and properties of raw 
refractory grade dolomite. Some of the 
data are included in table 3. The compo- 
sitions are similar to those for dolo- 
mites described by others (_5, 26-27) . 
However, besides compositional require- 
ments the physical properties, such as 
grain density, refractoriness, strength, 
and microstructure, of a refractory dolo- 
mite material are important. 



TABLE 3. - Composition and properties of refractory grade dolomites 







Chemica 


1 analy 


sis, wt 


-pet 


Physical properties 


Origin and formation 










Loss on 


Specific 


Bulk 


Poros- 




Si0 2 


1 R 2 3 


CaO 


MgO 


ignition 


gravity 


density, 
g/cm 3 


ity, 
pet 


GREAT BRITAIN 


















Dolomite (theoretical) 


NAp 


NAp 


30.41 


21.87 


47.72 


NAp 


NAp 


NAp 


Lower Permian systems: 




















0.33 


0.52 


30.63 


21.50 


47.37 


2.84 


2.47 


13.0 




.74 


.72 


30.25 


21.28 


47.00 


2.84 


2.41 


15.1 




.87 


.60 


30.32 


21.23 


47.13 


2.85 


2.39 


16.3 


Durham: Permian 




















.89 


.96 


30.6 


20.6 


46.95 


2.85 


2.53 


11.2 


South Wales: Carbon- 


















iferous limestone 4 ... 


1.28 


.81 


32.48 


19.41 


45.15 


2.82 


2.77 


1.8 


UNITED STATES 


















Ohio: Niagara system. 


.40 


.80 


30.1 


21.0 


47.20 


2.87 


2.66 


7.9 




.02 


.17 


30.6 


21.2 


47.50 


2.87 


2.55 


12.5 


Pennsylvania: Ledger 




















.30 


.65 


30.8 


21.1 


47.10 


2.84 


2.78 


2.1 


Missouri: Bonne Terre 




















.31 


3.73 


31.16 


19.2 


45.44 


2.84 


2.68 


6.0 



NAp Not applicable. 

1 R 2 3 = A1 2 3 + Fe 2 3 . 

2 Soft. 

^Medium to soft. 

4 Very hard. 



The quantity of dolomite produced for 
refractory uses is not a large portion of 
the total U.S. dolomite production. More 
than three-fourths of the dolomite quar- 
ried in the United States is used as an 
aggregate or a soil conditioner. In 1980 
( 19) , the production of refractory dolo- 
mite amounted to a total of 494,000 tons 
which was only 2.6 pet of the total lime 
and dolomite volume. The only States 
mentioned by Colby (_5) as producing re- 
fractory grade dolomite were Alabama, 
California, Colorado, Illinois, Michigan, 
Nevada, Ohio, Pennsylvania, Utah, and 
West Virginia. 

Ohio produces more dolomite than any 
other State and, in fact, produced ap- 
proximately 55 pet of the dead-burned 
dolomite consumed in the United States in 
1979 ( 9_) . While most of the major re- 
fractory companies in the United States 
produce their own raw materials for fire 
clay, high-alumina, and magnesia prod- 
ucts, they have not developed the facil- 
ities to handle refractory dolomite. Do- 
lomite materials are produced by five or 
six of the smaller companies. 

Unpublished information by a leading 
dolomite producer (10) indicates that the 
use of dolomite as a refractory was not 
popular in the United States until re- 
cently. Since about 1912, dolomite in 
the United States has only been produced 
with iron added to make fettling grain. 
Although used extensively as a refractory 
in Europe from the time of the Bessemer 
converter (1860's), high-purity dolomite 
was essentially unavailable in the United 
States as a refractory raw material until 
the early 1960's when both Basic, Incor- 
porated, and the J. E. Baker Co. began to 
produce a high-purity, high-density dolo- 
mitic grain. In Europe, on the other 
hand, very little fettling grain was pro- 
duced and nearly all the dolomite was 
produced as a high-density, high-purity 



refractory raw material. The greater 
shortage and higher price of high-quality 
magnesite in Europe, as compared with the 
United States, probably contributed to 
the earlier development of refractory do- 
lomite materials in Europe. 

U.S. DOLOMITE DEPOSITS 

Colby (_5) in 1941 and Weitz (26^) in 
1942 published extensive surveys on the 
dolomite resources of the United States 
and described the quantity, quality, and 
uses of the deposits of each State. The 
States with the most plentiful deposits 
of dolomite are Ohio, Indiana, Illinois, 
Wisconsin, Michigan, and Pennsylvania. 
Individual deposits are reported with re- 
serves varying from 10 to 350 million 
tons. Chemical analysis data are pre- 
sented for 212 deposits in Ohio, 18 in 
Indiana, 27 in Illinois, 111 in Wiscon- 
sin, 76 in Michigan, and 102 in Pennsyl- 
vania. All of these deposits are consid- 
ered to be high-grade dolomite materials 
that are defined by Weitz as material 
containing at least 98 pet total carbon- 
ates and less than 2 pet impurities in- 
cluding iron oxide, alumina, and silica. 

Additional information concerning dolo- 
mite resources is available in State 
Geological Survey publications of Cali- 
fornia, Illinois, Indiana, Michigan, Vir- 
ginia, West Virginia, and Wisconsin. The 
Alabama Geological Survey ( 25 ) reported 
that 11 dolomite quarries are in opera- 
tion primarily in the Birmingham area. 
Total reserves of these quarries are es- 
timated in billions of tons. Chemical 
analyses of these products indicated that 
most would be considered to be high-grade 
dolomites. The West Virginia Survey (27) 
provided information on limestone and 
dolomite quarries in that State. Only 
two of the quarries presently produce 
dolomite. 



DOLOMITE REFRACTORIES 



AGGREGATE PROCESSING 

The original refractory use of dolomite 
was in the uncalcined condition in open 



hearths or Thomas converters. As steel 
processing became better controlled, the 
need for calcined dolomite grain in- 
creased. Chesters (4) provides a good 



summary of the processing of dead-burned 
dolomite or "doloma," as it is called in 
England. The production of doloma fol- 
lows the reaction 

MgCa(C0 3 ) 2 + CaC0 3 + MgO + C0 2 (1) 



CaC0 3 + MgO + C0 2 
+ CaO + MgO + 2C0 2 . 



(2) 



This decomposition process is common- 
ly called calcination. Dolomite can be 
lightly calcined, as low temperature 
decomposition is called, or high fired 
to produce the dead-burned material. 
Production of higher purity dolomites, 
or low flux dolomites, has necessitated 
higher firing temperatures to produce 
dead-burned grain of satisfactory 
density. 

In the temperature range of 600° to 
900° C, the dissociation of dolomite re- 
sults in the intermediate formation of 
calcium carbonate and magnesia, but heat- 
ing above 900° C leaves only magnesia 
and lime as the products. On further 
heating, these oxides undergo crystal 
growth, the eventual size being very 
small in both cases. If reaction 2 is 
stopped immediately after the C0 2 is 
driven off, around 900° to 1,000° C, the 
product is too reactive and porous for 
use as a refractory raw material. There- 
fore, the calcination must be carried out 
at temperature of about 1,700° C in order 
to reduce the amount of porosity. 

Very tight control is needed in the 
manufacture of calcined dolomite, as re- 
fractories produced from it can suffer 
from one or the other of the following: 

1. Tendency to hydrate owing to reac- 
tion of free lime with moisture in the 
air. 

2. Tendency for "dusting" or disinte- 
gration owing to an inversion and volume 
change on cooling of dicalcium silicate 
formed in the material. 



The term "stabilization," as associated 
with dolomite refractories, has been used 
to cover the following three procedures: 

1. The coating of calcined dolomite 
with pitch to reduce the rate of 
hydration. 

2. The conversion of free lime to a 
silicate or ferrite to reduce hydration. 

3. The addition of boric acid, phos- 
phates, or other "stabilizers" to prevent 
the inversion of dicalcium silicate. 

It would appear better to use the word 
"stabilization" solely for the last two 
procedures. 

In a Bureau of Mines publication in 
1942, Schallis (20) presented a survey on 
the calcination of raw dolomite. Partic- 
ular mention is made of the hydration 
problem of dead-burned dolomite. Methods 
such as coating with tar or covering with 
treated paper have been successful in 
permitting storage for a few weeks or 
even a few months. To aid calcination, 
help stabilize the calcium oxide, and im- 
prove its ability to sinter, iron oxide 
was added to dead-burned dolomite before 
the charge went to the kiln. Also, it 
has been found that the conversion of the 
lime into dicalcium and tricalcium sili- 
cates by the addition of silica will re- 
duce the hydration tendency of the lime. 

Unfortunately, tricalcium silicate will 
break down into lime and beta dicalcium 
silicate, which is not volume stable and 
tends to disintegrate. In order to sta- 
bilize the dicalcium silicate, iron oxide 
can be added to the dolomite. Seil (21- 
23 ) received several patents directed 
toward stabilization of dead-burned dolo- 
mite grains by incorporating specified 
additions of Si0 2 and A1 2 3 as a means of 
reducing hydration tendencies. Similar- 
ly, Lee ( 13 ) patented processes for the 
formation of low melting liquid phases in 
dolomite refractories in order to improve 
hydration resistance. 



While the use of so-called "stabilized" 
dead-burned dolomite was extensive in the 
past, this practice is not in widespread 
use today. One reason for this fact is 
that the silica and iron oxide additions 
reduce the refractoriness of dolomite; 
another reason is that producers and con- 
sumers of dolomite materials have devel- 
oped better handling methods for reducing 
hydration. 

Most of the dolomite used for refrac- 
tories is produced in either shaft kilns 
or rotary kilns. Both types are normally 
fired with gas or oil. Some European 
shaft kilns have been operated like blast 
furnaces, using alternating layers of raw 
dolomite and coal. Prior to firing, the 
dolomite is crushed and screened to a 
size suitable for feeding to the kiln. 
Material for feeding to shaft kilns is 
usually between 50 and 150 mm while mate- 
rials for feeding to a rotary kiln is 
usually between 3 and 40 mm. In both 
cases, the crushed feed is washed with 
water to remove fine particles, particu- 
larly clay contaminations. The thermal 
processes can be considered as divided 
into the following four stages: drying; 
calcination, yielding a porous mixture of 
lime and magnesia; burning, in which po- 
rosity is greatly reduced; and cooling, 
which mainly serves to preheat incoming 
air. 

Lee ( 14) , in 1962, described a means to 
achieve higher firing temperatures and 
higher heating efficiencies by the use of 
insulating brick as a backup lining and 
the use of oxygen additions to the com- 
bustion air. An addition of high-purity 
oxygen comprising 3 to 10 pet of the 
total oxygen in the enriched combustion 
air is adequate to give the firing condi- 
tions necessary to produce dense grain. 

A. recent departure from this conven- 
tional single-stage firing process has 
been the introduction of a two-stage fir- 
ing process involving a pelletization or 
high-pressure briquetting stage. This 
process is particularly useful for pro- 
ducing high-density grain from dolomites 
that are difficult to dead-burn to a high 
density in a single-stage process. The 



dolomite is first decomposed to produce a 
reactive oxide that is then pelletized 
and dead-burned in a rotary or shaft kiln 
to densities of 3.20 to 3.30 g/cm 3 . 

As described by Obst ( 17) , it is also 
possible to produce magnesia-dolomite 
clinkers (coclinkers) by mixing the reac- 
tive oxide with reactive magnesium oxide 
before pelletization. These clinkers can 
have MgO contents from 50 to 80 pet. The 
amount of direct bonding between the per- 
iclase grains increases in proportion to 
the MgO content. Coclinkers has all the 
advantages and disadvantages of dolomite, 
but has a higher MgO content. It is pre- 
ferred to achieve the MgO enrichment by 
addition of calcined MgO grains, espe- 
cially in the fine fraction. 

Chesters (40 compared the chemical com- 
positions of British dolomites and those 
of other dead-burned materials. Results 
of this comparison are given in table 4. 
Present-day commercial dead-burned dolo- 
mite contains small amounts of silica, 
alumina, and iron oxide as accessory ox- 
ides. The iron oxide is usually present 
as the ferric form and will combine with 
lime to form dicalcium ferrite. Usually 
a small amount of iron will exist as FeO. 
The ratio of ferric to ferrous oxide will 
depend on the firing temperature and com- 
bustion conditions in the kiln. Alumina 
is not reduced under ordinary conditions 
and forms mineral phases that have low 
melting temperatures. Therefore, it is 
desirable to keep the alumina contents of 
dolomite refractories relatively low. 

The overall chemistry as well as the 
ratio of accessory oxides to the combined 
MgO and CaO content affect both physical 
and chemical resistance of dead-burned 
dolomite grains. Since the majority of 
dolomite grains are used in the form, of 
organically bonded brick or specialty 
mixes, this is the logical form in which 
to measure hydration resistance. Hubble 
(8) devised a hydration test that led to 
the establishment of a standard test, 
ASTM C492-66 (2^). Dolomite material of a 
plus 35-mesh size was placed in a cabinet 
at a temperature of 71° C and relative 



TABLE 4. - Typical properties of dead-burned dolomite grains 





Chemi 


cal ana 


lysis , 


wt-pct 


MgO, by 
difference, 


Bulk 


Origin 


Si0 2 


A1 2 3 


Fe 2 3 


CaO 


density, 












wt-pct 


g/cm 3 


England: 
















2.50 


1.21 


1.64 


57.60 


37.05 


3.00 




2.35 
2.58 


1.42 
1.30 


1.40 
1.67 


58.20 
56.06 


36.12 
38.39 


2.85 


South Wales 


3.00 




.88 


.45 


1.30 


56.80 


40.57 


3.10 




.83 


.44 


1.14 


56.70 


40.89 


3.25 




1.00 


.30 


1.50 


NAp 


] 36.0 


3.15 




1.05 


.92 


.28 


56.10 


41.50 


3.20 




.70 
.60 


.45 
.60 


.60 
3.00 


57.20 
62.50 


41.05 
33.30 


3.10 




3.00 


United States (low flux) 


.40 


.30 


.30 


56.90 


40.40 


3.25 


United States (standard) 


1.10 


.60 


1.20 


51.80 


38.0 


3.20 



NAp Not applicable. 1 Minimum. 



humidity of 85 pet. After 24 hr, the 
material was removed, dried, and screened 
at 35 mesh to determine the amount of 
material passing through. The rate of 
hydration was found to be dependent on 
the heat treatment the dolomite had re- 
ceived, on the amount of iron oxide in 
the dolomite, on the dolomite grain siz- 
ing, and on the number of broken grains 
present. 

BRICK PROCESSING 

The majority of dolomite brick is used 
in the form of either pitch-bonded or 
tempered, although others are of the 
burned-impregnated type. A limited num- 
ber of fired dolomite brick containing no 
carbon are used in rotary cement kiln 
linings and electric furnace linings, 
although direct-bonded magnesia-chrome 
bricks have generally been the accepted 
refractory products for both these appli- 
cations. Kappmeyer (11) presented a sur- 
vey of the carbon-containing types of 
bricks. The processing of the unburned 
types consists of preheating the sized 
refractory grain and the pitch material 
separately, mixing these two materials in 
a heated mixer, and pressing brick shapes 
at 4,000 to 10,000 psi on mechanical 
presses. 



the brick. Generally, to obtain the de- 
sired combination of maximum brick den- 
sity and maximum residual carbon, the 
amount of pitch will be 5.0 to 6.75 wt- 
pct. The type of pitch has an important 
influence on the strength of the brick at 
the low temperatures associated with part 
of the burn-in cycle. Brick with exces- 
sive pitch has low strength for a short 
time at low temperatures and has col- 
lapsed under its own weight. 

After the brick is pressed, it is 
cooled for storage or taken directly to 
ovens for tempering. Tempering of the 
pitch-bonded brick improves several char- 
acteristics. The low-temperature hot 
strength of the brick is markedly in- 
creased, eliminating concern about possi- 
ble failure of the lining during burn-in. 
Also, tempering results in a significant 
improvement in the resistance of the 
brick to hydration. By tempering, the 
safe storage period for dolomite brick 
can be extended from only a few days to 
several weeks. The temperatures involved 
in tempering generally range from about 
90° to 650° C, but are more commonly 230° 
to 315° C. Exposure times range from 
30 min to 48 hr, with the shorter time 
being associated with the higher 
temperatures. 



The amount of pitch varies and is an 
important influence on the properties of 



Pitch-impregnated brick is produced by 
forcing pitch into the open pores of a 



presintered (burned) brick made from do- 
lomite grain aggregates. The properties 
of the burned brick may vary widely ac- 
cording to composition and degree of heat 
treatment before impregnation. The 
burned brick may be impregnated with 
pitch to some extent simply by dipping 
the brick into liquid pitch at 120° to 
315° C, but more commonly it is impreg- 
nated by using a vacuum pressure system 
to accelerate the rate at which the pitch 
is forced into the brick pores. 

The quantity of pitch picked up by a 
brick is directly related to the initial 
porosity of the brick. The residual car- 
bon content in the brick naturally in- 
creases with greater pitch content and/or 
increased pitch softening point. How- 
ever, because brick porosity is confined 
to a narrow range to achieve other desir- 
able properties, the quantity of pitch 
that can be introduced is limited. With 
this limitation, it is desirable to use 
pitch with the highest softening point 
compatible with the operating character- 
istics of the vacuum impregnating system. 

It is interesting to compare the amount 
of energy required to produce tempered 
brick with that required for impregnated 
brick. Production of impregnated brick 
requires 1.64 million Btu/ft 3 which is 20 
to 30 pet more energy than for the same 
volume of tempered brick (1.35 million 
Btu). Also, experience indicates that 
properly made tempered brick can give 
service life equivalent to that of the 
impregnated, burned brick. 

BRICK USAGE 

United Kingdom 

Leonard (15) reviewed BOF lining prac- 
tices in the United Kingdom. Both dolo- 
mite and magnesite were used. There has 
been a trend towards magnesia enrichment 
of dolomite refractories by additions of 
magnesite. Improvements in the quality 
of dead-burned dolomite and bricks made 
from it were achieved by more selective 
quarrying and blending of deposits and 
the greater use of rotary kilns and shaft 
kilns with higher firing temperatures. 



It became possible to produce grain of 
such consistent chemistry and density 
that silica content was restricted to 
1 pet and densities of over 3.0 g/cm- 5 
were achievable. 

Spencer (24) reported that in 1970, 
pelletized dead-burned dolomite grain was 
introduced in England. This arose be- 
cause most of the highest purity dolomite 
in the United Kingdom is difficult to 
sinter to high densities in a single fir- 
ing process. The decomposition of high- 
purity dolomite to an active oxide fol- 
lowed by pelletizing under high pressures 
and sintering results in densities in the 
3.25- to 3.30-g/cm- 5 range. Of course, 
this two-stage firing process has the 
disadvantage of increased costs. With 
the introduction of this pelletized dead- 
burned dolomite, linings gave improved 
furnace performances of approximately 10 
to 15 pet. 

Europe 

Hardy (6.~Z_) discussed BOF linings and 
lining wear from the standpoint of a 
steelmaking consumer. In Europe, a long 
history of basic Bessemer steelmaking re- 
sulted in the establishment of raw dolo- 
mite as standard lining materials. The 
first major change in usage patterns came 
with the advent of big capacity furnaces. 
The danger of slumping during burn-in is 
greater with big vessels and, therefore, 
almost all vessels in Europe of 200-ton 
capacity or more used tempered blocks. 
Magnesia-enriched tempered dolomite and, 
in some cases, tempered magnesite have 
been used in selected zones to combat 
slag attack. 

Japan 

Hardy (6^) and Leonard (15) both de- 
scribed the improvements in Japanese 
steel refractories. In Japan, which 
lacks suitable reserves of most raw mate- 
rials, the practice has been to use syn- 
thetic magnesia-dolomite clinkers and 
seawater periclase in BOF refractories. 
From the late 1950's until about 1970, 
the average MgO content of BOF linings 
increased from 50 to 60 pet up to 80 to 



90 pet. This is indictive of increased 
usage of high magnesia coclinkers and of 
seawater periclase. In 1976, refractory 
consumption in BOF vessels of enriched 
dolomite was about one-half that of peri- 
clase. Dolomite bricks were initially 
pitch-bonded, but fired mixtures with 
periclase were introduced in the late 
1960*s. By the early 1970* s, the use of 
MgO-enriched dolomite was well advanced, 
first as pitch-bonded, then as fired 
brick. In Japan, both slag testing and 
thermal shock resistance testing have 
been used for evaluating refractories for 
BOF linings. Both authors stress the ex- 
tremely long lining lives, over 1,000 
heats, being achieved in Japanese steel 
plants resulting, in part, from strict 
control of slag chemistry and gunning 
maintenance. 

United St ates 

It is logical to discuss dolomite brick 
usage in terms of iron and steelmaking 
since this usage constitutes between 50 
and 70 pet of the total output of the re- 
fractories industry. Kappmeyer (12) es- 
timated that of refractories used in the 
steel industry, about 3 pet are consumed 
in coke ov Q ns , 10 pet in blast furnaces, 
60 pet in BOF's, 12 pet in pouring pits, 
and 15 pet in continuous casting, rol- 
ling, and other forming operations. 
World steel production, broken down by 
process, is shown in table 5. It is 
interesting to observe the change in 
types of refractories used in the BOF 
steelmaking process. Table 6 presents 
the approximate distribution of BOF brick 
used in the United States. 

TABLE 5. - Distribution of steel 
production by process, million 
tons (12) 



TABLE 6. - Approximate distribution 
of BOF brick usage in the United 
States, percent (12) 



Process 


1960 


1971 


1985 




47 

261 

13 

39 


21 
230 
272 

94 


10 




90 


B0F/0-B0F 


850 




240 








379 


627 


1,200 



Brick 


1967 


1970 


1980 


Burned impregnated 


10 

32 
41 
17 


30 

29 
24 
17 


40 
20 


Magnesite, all types... 
Dolomite, all types.... 


25 
15 



Some other processes are included in 
the total. 



Kappmeyer (11) compared the properties 
of dolomite-containing steel plant re- 
fractories of both the tempered and 
burned-impregnated types. These property 
comparisons are shown in table 7. While 
the burned brick has lower levels of re- 
sidual carbon, this type shows higher re- 
sistance to slag erosion. Although few 
dolomite-containing brick are used in the 
burned condition, substantial amounts are 
used as pitch-bonded or tempered. 

In 1980, Marr ( 16) surveyed the appli- 
cations of dolomite materials as refrac- 
tories. Marr stated that dead-burned 
dolomite is used in the form of both 
monolithic products and brick products. 
Dolomite gunning mixes have been used 
extensively, especially in electric arc 
furnaces. Hearths of both open hearth 
and electric furnaces have been made of 
rammed dolomite. Tar-bonded dolomite 
bricks have been found to be satisfactory 
for BOF linings particularly when used in 
combination with magnesite bricks. The 
combining of continuous casting and ladle 
refining processes in steelmaking is com- 
mon now and results in higher ladle oper- 
ating temperatures and basic slags. 
Therefore, traditional clay and alumina 
bricks are being replaced by basic prod- 
ucts, quite often, dolomite. 

Other applications in which fired dolo- 
mite brick has performed well are argon- 
oxygen-decarburization (AOD) furnaces, 
cement and lime rotary kilns, and nickel 
or copper refining smelters. 

The swing to low-cost dolomite brick 
in the United States never reached the 

level predicted around 1965. Peatfield 
and Spencer (18), in 1979, in discussing 



10 



TABLE 7. - Dolomite brick properties 





Chemical compc 


jsition, 


Bulk 


Hot modulus 


Residua! 


. carbon 


Slag 


Brick, type 




wt-pct 




den- 
sity, 

g/cm 3 


of rupture, 
psi 


content, wt-pct, 
after coking to — 


ero- 


and sample 


MgO 


CaO 


Fe 2 3 


A1 2 3 


Si0 2 


sion 1 




1,200° C 


1,980° C 


1,090° C 


1,650° C 




Tempered 
























dolomite: 
























TD-1 


40. A 


56.9 


0.3 


0.3 


0.4 


2.84 


NAp 


NAp 


3.8 


2.6 


2.4 


TD-2 


40.0 


55.9 


.0 


.2 


.8 


2.84 


NAp 


NAp 


3.4 


2.7 


2.5 


TD-3 


40.2 


55.6 


.9 


.2 


.6 


2.84 


NAp 


NAp 


3.4 


2.7 


3.2 


TD-4 


40.8 


56.5 


.2 


.1 


.3 


2.84 


NAp 


Nap 


3.7 


2.5 


3.6 


Tempered 
























dolomite 
























peri- 
























clase: 
























DPT-1... 


60.2 


37.9 


.3 


.3 


.6 


2.96 


NAp 


NAp 


Nap 


2.8 


Nap 


DPT-2. . . 


57.5 


37.4 


3.3 


.5 


2.0 


3.01 


NAp 


NAp 


NAp 


2.6 


NAp 


DPT-3... 


61.2 


36.1 


.6 


.3 


1.4 


2.95 


NAp 


NAp 


NAp 


3.0 


NAp 


Burned im- 
























pregnated 
























dolomite: 
























TD-1 


40.8 


57.9 


.2 


.2 


.6 


3.14 


1,865 


610 


NAp 


1.5 


1.3 


ID-2 


42.0 


55.5 


.3 


.5 


.6 


3.06 


1,080 


550 


NAp 


.9 


1.2 


ID-3. ... 


40.2 


55.6 


.8 


.2 


.6 


3.04 


1,860 


380 


NAp 


.8 


1.1 


Burned im- 
























pregnated 
























dolomite 
























peri- 
























clase: 
























IDP-1... 


66.9 


31.6 


.1 


.2 


1.2 


2.98 


910 


680 


NAp 


1.3 


1.1 


IDP-2. . . 


60.0 


38.3 


.2 


.2 


.7 


3.12 


865 


370 


NAp 


1.5 


.8 



Nap Not applicable. 
Relative depth of brick eroded away as compared with established standards. 



basic raw materials for steelmaking 
refractories, mentioned that dolomite- 
and magnesia-based materials are the only 
materials that are readily available and 
cost effective. The selection between 
magnesia- and dolomite-based products de- 
pends not only on the technical merits of 
the materials and lining life require- 
ments, but also on their relative econo- 
mies. For example, magnesia products in 



the United States are only 40 to 50 pet 
more expensive than dolomite products, 
whereas in Europe, they are 200 to 
300 pet more expensive. This reason has 
been quoted for the greater development 
of dolomite in England. The absence in 
the United States of a strong basic Bes- 
semer tradition is probably another im- 
portant reason. 



PROPERTIES OF 14 U.S. DOLOMITES 



MATERIALS AND TEST PROCEDURES 

Samples of 14 different raw dolomite 
samples were obtained from sources in 
Alabama, Ohio, Pennsylvania, Missouri, 
Michigan, California, and Wisconsin. 
Eight of these materials were obtained 
from suppliers of refractory grade 



dolomites, while the other six were rep- 
resentative of dolomites that are used 
for nonref ractory applications. Approxi- 
mately 50 lb of each sample was received. 
Representative portions of each sample 
were used in the various characterization 
studies. Powdered samples were sent to 
an independent analytical laboratory for 



chemical analysis and loss on ignition 
(LOI) determinations according to the 
procedures of ASTM 0574-71. Mineralogi- 
cal analyses were conducted on minus 
325-mesh material by X-ray diffraction. 
Differential thermal analysis (DTA) and 
thermogravimetric (TGA) curves were ob- 
tained on the materials using a commer- 
cially available thermal analyzer. Ap- 
parent specific gravities were measured 
using an air comparison pycnometer. Pe- 
trographic analyses and cathode- 
luminescent photographs were made on thin 
sections from each material. 

RESULTS AND DISCUSSION 

The results of the chemical analyses 
and loss on ignition, apparent specific 
gravity, and mineralogical determinations 
are shown in table 8; petrographic analy- 
sis data are given in table 9. All 14 of 
these samples meet the chemical require- 
ments for refractory grade dolomites as 
specified in table 2. Only three of the 



11 



samples had impurity contents totaling 
over 2.0 wt-pct with the major impurities 
being either Si02 or Fe 2 03. The theoret- 
ical LOI value for pure dolomite is 47.72 
wt-pct. All of the samples had LOI val- 
ues over 45.0 wt-pct, and seven had LOI 
values greater than 47.0 wt-pct. The 
most predominant accessory minerals were 
quartz and calcite. The apparent spe- 
cific gravity values were all between 
2.81 and 2.87. This property measure- 
ment, when greater than 2.80, is usually 
a good indication of dolomite that can be 
fired to high-grain density. 

Photomicrographs of four of the samples 
are shown in figures 1 through 4. These 
photomicrographs illustrate the wide 
range in grain sizes and microstructures 
of the various dolomites. 

The micros tructure of sample Ohio No. 1 
(fig. 1) is characterized by small grains 
(average diameter of approximately 100 
ym) having no twinning and with poorly 



TABLE 8. - Properties of raw domestic dolomites 



Source 

and 
sample 



Chemical analysis, wt-pct 



MgO 



CaO 



SiO- 



A1 2 2 



Fe 2 3 



Loss on 
ignition 



Apparent 
specific 
gravity, 
g/cm 3 



Accessory 
mineral 
phases 1 



Hydra- 
tion, 2 
wt-pct 



Calculated 
liquid 
phase, 
wt-pct 



Alabama : 

1 

2 

3 

Ohio: 

1 R 

2 R 

3 R 

Pennsyl- 
vania: 

1 R 

2 R 

3 

Michigan: 

1 

2 

Missouri : 

1 R 

Wisconsin: 

1 

Califor- 

nia: 1.. 

R Ref ractor 

Q, quartz 



20.80 
20.39 
20.12 

21.20 
19.46 
20.99 



21.26 
21.01 
21.22 

21.18 
20.95 

19.20 

21.16 

21.70 



30.19 
30.13 
30.52 

30.61 
29.57 
30.13 



27.61 
30.76 
30.83 

30.61 
30.34 

31.16 

30.78 

31.07 



.12 
.11 
.48 

.02 
.69 
.40 



.16 
.29 
.15 

.49 
.52 

.31 

.27 

.50 



0.56 
.39 
.82 

.11 
.83 
.68 



.06 
.22 
.20 

.08 
.08 

.12 

.04 

.07 



0.22 
.31 
.27 

.06 

2.99 

.12 



.30 
.39 
.22 

.10 
.19 

3.61 

.18 



46.68 
47.30 
46.47 

47.54 
45.05 
47.26 



46.41 
47.08 
47.06 

47.19 
47.42 

45.44 

46.95 



.15 45.85 



2.87 
2.86 
2.85 

2.87 
2.84 
2.87 



2.85 
2.86 
2.81 

2.84 
2.84 

2.84 

2.86 

2.82 



Q,C 

Q 
Q,C 

Q 
Q 
Q 



Q 

Q,C 

c 

Q,C 
Q,C 

Q,C 

Q,C 

Q,C 



83.5 
80.9 
48.4 

100.0 

ND 

100.0 



72.6 
95.1 
58.3 

98.6 
ND 

5.4 

99.5 

98.8 



10.4 

9.8 

15.2 

.5 

8.9 

2.3 
4.2 
2.3 

4.6 
ND 

13.8 

2.3 

4.2 



y-grade dolomi 
; C, calcite. 



te. ND 
2 As dete 



Not determined, 
rmined per ASTM 



C492-66 (1981). 



12 



TABLE 9. - Petrographic analysis data for raw domestic dolomites 



Source and 


Crystal- 


Grain 


Formation 


General description 


sample 


Unity 1 


size, ram 


and age 




Alabama: 










1 


1 


0.06 -0.18 




'Patchy areas of coarse crys- 
tals, not equigranular , some 
dark organic material. 




1 


.25 -1.25 


> Ketona, Upper 


^Equigranular, curved grain 








Cambrian. 


boundaries, no trace of orig- 
inal texture. 


3 


1 


.18 -1.25 




Coarse crystals along frac- 
tures, not equigranular, no 
trace of original texture. 


Ohio: 










1 R 


1 


.04 - .18 




Not equigranular, patchy zones 
of coarse crystals, porous. 










2 R 


1 


.125- .375 


Guelph, 
Silurian. 


Not equigranular, contacts 
wavy, slightly dirty, organic 
I material along stylolites, 
















voidy . 


3 R 


1 


.06 - .375 




Equigranular, dirty, wavy con- 
tacts, porous, pores may con- 
„ tain organic material. 


Pennsylvania: 










1 R 


P 


.06 - .375 




'Not equigranular, irregular 










grain boundaries, wavy grain 










boundaries with cloudy 








Ledger, Lower 


centers. 


2 R 


P 


.125-1.0 


> Cambrian. 


s Some circular patches of fine 
grains, some pressure-induced 












twinning; no indication of 










original texture. 


3 


P 


.125-1.0 






Michigan: 




1 


P 


.06 - .18 


1 Engadine, 
I Middle 


f Equigranular , wavy contacts, 
I porous, dirty. 


2 


P 


.125- .75 


Silurian. 


[ Do. 


Missouri: 1 R 


I 


.06 - .375 


Bonne Terre, 
Upper 
Cambrian. 


Not equigranular, excellent 
zoning, could be areas of 
iron, very cloudy, an altered 
subtidal limestone, perhaps 
oolitic circular patterns. 


Wisconsin: 1 


I 


.04 - .675 


Niagara, Middle 
Silurian. 


Finely crystalline, poorly 
sorted crystals, not equi- 
granular, no trace of origi- 
nal structure. 


California: 










I 


P 


1 -5 


Sur, Jurassic. 


Coarsely crystalline, twinned, 
equigranular contacts 












straight, clear crystals. 


Rof raphnr \r—cr v 


a A a <^r>1 Ami 


t- a 1 T -i T-i ^ c 


^ mmck i^i aha* T> haay 





13 




FIGURE 1. - Photomicrograph of Ohio dolomite No. 1 presently used to produce refractory products. 




FIGURE 2. = Photomicrograph of Missouri dolomite presently used to produce refractory products, 




K.4-'. JpiO 0.2,,;. 

'' "^ I I %$ 

>■ / ^il $wl», mm |jS 




FIGURE 3. - Photomicrograph of Alabama dolomite No. 3. 




FIGURE 4. - Photomicrograph of Pennsylvania dolomite No. 3, 



15 



defined grain boundaries. The micro- 
structure of sample Missouri No. 1 (fig. 
2) consists of medium-sized grains (aver- 
age diameter of approximately 300 ym) 
having no twinning and with better de- 
fined grain boundaries. The microstruc- 
ture of sample Alabama No. 3 (fig. 3) 
consists of large, angular grains (aver- 
age diameter of approximately 600 ym) 
having no twinning and with well-defined 
boundaries. The microstructure of sample 
Pennsylvania No. 3 (fig. 4) consists of 
large, angular grains (average diameter 
of approximately 750 ym) having a large 
number of twinned grains or striations 
and with well-defined grain boundaries. 

Of the 14 raw dolomites characterized 
in this investigation, only two (Pennsyl- 
vania No. 2 and 3) are suitable for cal- 
cining to high-density, dead-burned grain 
in a single-step firing process. While 
these two samples did not exhibit any 
marked differences from the other dolo- 
mite samples with regard to chemistry, 
mineralogy, or thermal decomposition, 
they contain the largest grain sizes of 
all the materials observed. Besides hav- 
ing grains that are approximately twice 
the size of those of most of the other 
samples, these two samples also contain a 
large number of twinned grains , as can 
be seen in figure 4. While it cannot be 
assumed that either the larger grain size 
or the twinned grains have any influence 
upon the calcination and densif ication 
characteristics of these two dolomite 
samples, further investigations into the 
fired grain processing and properties may 
provide the answers. 

Examples of the thermal analysis data 
are shown in figures 5 through 7. With 
regard to DTA data, it is possible to 
group the dolomites by the similarities 



in the endothermic peak locations, as has 
been done with the curves in figure 6. 
Thus, it is evident in figure 6 that 
three of the Alabama materials behave 
similarly upon heating. Comparing the 
DTA curves in figure 5, it is seen that 
the two Michigan dolomites have large 
peaks around 880° C as do most of the 
other dolomites, but both of the Michigan 
materials have a small peak around 
650° C, which none of the other materials 
exhibit. All the DTA curves for these 
materials indicate typical endothermic 
peaks exhibited by most dolomite mate- 
rials. The sharper, lower temperature 
peak ranging from 780° to 820° C corre- 
sponds to the decomposition of MgC0 3 , and 
the broader, higher temperature peak 
ranging from 860° to 920° C corresponds 
to the decomposition of CaC03 . 

Examples of typical TGA curves are 
shown in figures 8 and 9. While the DTA 
curves have separate peaks representing a 
two-step decomposition process , the TGA 
curves , which were run at half the heat- 
ing rate of the DTA scans , indicate only 
a single step decomposition. The total 
weight losses for these dolomites coin- 
cide well with the LOI values reported in 
table 8. The TGA weight loss for Michi- 
gan dolomite No. 1 was 47.62 wt-pct ver- 
sus 47.19 wt-pct LOI, and the TGA weight 
loss for Pennsylvania dolomite No. 2 was 
47.78 wt-pct versus 47.08 wt-pct LOI. 

It is anticipated that when the refrac- 
tory properties of the calcined grain 
produced from the 14 different dolomites 
are determined that these properties 
can be related to differences in the 
chemical compositions, and especially the 
differences in microstructure and thermal 
decomposition of the raw dolomites. 



SUMMARY 



A review of the literature on dolomite 
resources showed that large quantities of 
high-purity dolomite materials exist in 
the United States. Most of these depos- 
its are located in the area around the 
Great Lakes as well as in Pennsylvania, 
Alabama, California, and West Virginia. 



Many of these resources have been used to 
provide dolomites suitable for various 
uses other than refractory products. A 
few of the deposits have proven useful as 
refractory grade dolomites. Besides 
meeting requirements for high purity lev- 
els, refractory grade dolomites also must 



16 




600 640 680 720 760 800 840 880 920 960 1,000 



TEMPERATURE, ° C 

FIGURE 5. - DTA curves for six dolomites. 




600 640 680 720 760 800 840 880 920 960 1,000 



TEMPERATURE, ° C 

FIGURE 6. - DTA curves for five dolomites. 




600 



640 680 720 760 800 840 880 920 960 1,000 



TEMPERATURE, ° C 

FIGURE 7. - DTA curves for three dolomites. 

meet requirements for high grain density 
and resistance to hydration. 

The ideal refractory grade dolomite 
material is one that can be calcined in a 
single pass through a kiln. Since very 
few such sources are available, some do- 
lomite producers have introduced a two- 
step firing process consisting of a low- 
temperature calcination followed by bri- 
quetting and a high-temperature firing. 
The double-firing process adds signifi- 
cantly to the price of the resultant 
grain. 

Another product that dolomite producers 
have developed is an MgO-enriched do- 
lomite coclinker. By adding periclase 



120 

no 

« 100 

o. 

O 90 

LU 

2 80 

a. 

s 
< 

" 70 
60 



KEY 

PENNSYLVANIA DOLOMITE N0.2 

( ) Sample weight 

{ ) Derivative 



' L. 



100 200 




300 400 500 600 
TEMPERATURE, ° C 



700 800 900 1,000 



FIGURE 8. - TGA curve for a sample of Penn- 
sylvania dolomite No. 2. 

powder to the dolomite before the bri- 
quetting operation, a grain of higher MgO 
content and thus improved slag resistance 
can be produced. 

The European countries, especially Eng- 
land, have led in the increased usage of 
dolomite refractories. This fact has 
been attributed to the greater price dif- 
ferential between dolomite and periclase 
in Europe versus the United States and to 
a traditionally greater use of Bessemer 
converters for steelmaking in Europe. 

An investigation of 14 raw domestic do- 
lomites was conducted with the purpose 
of characterizing these materials and 
comparing their properties with the 



17 



120 
110 
100 



5 90 

UJ 

uj 80 

s 

< 



60 



1 I " I ' I ' — 

KEY 
MICHIGAN DOLOMITE NO 

( ) Sample weight 

(---\ Derivative 




so]— — ' ■ ' ■ ' ■ ' ■ ■ ' L ' ' ' ' ■ ' ' , '- 2 



E 
2 a 



1 < 
> 



100 200 300 400 500 600 700 800 900 1,000 
TEMPERATURE, ° C 

FIGURE 9. TGA curve for a sample of Michi- 
gan dolomite No. 1 . 

refractory properties of calcined grain 
produced from them. The raw materials 
were characterized as to chemical, physi- 
cal, and thermal properties. All of the 
materials contained at least 49.0 wt-pct 
combined MgO and CaO. Raw apparent spe- 
cific gravities ranged from 2.81 to 2.87 
and the raw bulk densities ranged from 
2.55 to 2.80 g/cm 3 . The major accessory 
minerals associated with these dolomites 
were calcite and quartz. 



The thermal analyses of the materials 
were characterized by two endothermic 
peaks, one occurring between 780° and 
820° C and the other occurring between 
860° and 920° C. Examination of thin 
section photomicrographs of the raw dolo- 
mites indicated that the average crystal- 
lite grain size ranged from around 100 ym 
up to about 750 urn. The microstructures 
of two Pennsylvania dolomites that are 
suitable for calcining to high density 
dead-burned grain in a single firing were 
characterized by the largest average 
crystallite grain sizes and by a large 
number of twinned grains. It is possible 
that the large grain sizes and occurrence 
of twinned grains has some influence upon 
the calcination and densif ication of 
these dolomites. Further investigations 
into fired grain processing and proper- 
ties may resolve this question. 

With the large reserves of high purity 
dolomite in the United States and the 
price advantage that dolomite holds over 
seawater periclase, it appears that the 
U.S. refractory practice should move 
toward higher dolomite usage. 



REFERENCES 



1. American Society for Testing and 
Materials. Standard Classification of 
Granular Refractory Dolomite. C468-70 in 
1981 Annual Book of ASTM Standards: 
Part 17, Refractories, Glass, Ceramic 
Materials; Carbon and Graphite Products. 
Philadelphia, PA, 1981, pp. 383-384. 



4. Chesters, J. H. Refractories: Pro- 
duction and Properties. The Iron and 
Steel Institute. London, 1973, 553 pp. 

5. Colby, S. F. Occurrence and Uses 
of Dolomite in the United States. 
BuMines IC 7192, 1941, 21 pp. 



2. 



Standard Test Method for 



Hydration of Granular Dead-Burned Refrac- 
tory Dolomite. C492-66 in 1981 Annual 
Book of ASTM Standards: Part 17, Refrac- 
tories, Glass, Ceramic Materials; Carbon 
and Graphite Products. Philadelphia, PA, 
1981, pp. 404-405. 



6. Hardy, C. W. , and A. J. Owen. De- 
velopment of Refractory Linings to Meet 
Operational Requirements in Oxygen 
Vessels. Proc. Conf. on Basic Oxygen 
Steelmaking: A New Technology. The 
Metals Society, London, May 1978, 
pp. 123-130. 



3. Carr, D. D. , and L. F. Rooney. 
Limestone and Dolomite. Ch. in Ind. 
Miner, and Rocks, American Institute of 
Mining, Metallurgical, and Petroleum En- 
gineers. New York, 1975, 1,360 pp. 



7. Hardy, C. W. B0F Refractories — A 
Question of Continuity. The Refractory 
J., November 1972, pp. 9-17. 



18 



8. Hubble, D. H. , and W. J. Lackey. 
Hydration Test for Dead-Burned Dolomite. 
Am. Ceram. Soc. Bull., v. 41, No. 7, 
1962, pp. 442-446. 

9. Industrial Minerals Consumer Sur- 
vey. Raw Materials for the Refractories 
Industry — Dolomite, High Performance at 
Low Cost. Metal Bull., Ltd., London, 
1981, pp. 57-65. 

10. J. E. Baker Co. Unpublished in- 
formation compiled by technical staff. 
September 1981, 71 pp.; available upon 
request from J. E. Baker Co., York, PA. 

11. Kappmeyer, K. K. , and D. H. Hub- 
ble. Pitch-Bearing MgO-CaO Refractories 
for the BOP Process. Ch. in High Tem- 
perature Oxides, ed. by A. M. Alper. 
Academic Press, Inc., New York, 1970, 
358 pp. 

12. . Trends and Challenges in 

the Future of Steelplant Refractories. 
Ironmaking and Steelmaking, v. 3, No. 3, 
1976, pp. 113-128. 



a Basic Refractory Material. Proc. 
Brit. Ceram. Soc, No. 28, June 1979, 
pp. 225-241. 

18. Peatfield, M. , and D. R. F. Spen- 
cer. Developments in Refractory Materi- 
als for LD Linings. Ironmaking and Steel- 
making, v. 6, No. 5, 1979, pp. 221-234. 

19. Pressler, J. W. Lime. BuMines 
Minerals Yearbook 1980, v. 1, pp. 507- 
518. 

20. Schallis, A. Dolomite-Base Re- 
fractories. BuMines IC 7227, 1942, 
11 pp. 

21. Seil, G. E. High Melting Point 
Silicate Refractory. U.S. Pat. 
2,207,557, July 9, 1940. 

22. _. Preparation of Refractory 
Material^ U.S. Pat. 2,207,072, July 9, 
1940. 



23. 



. Corrected Basic Refractory. 



U.S. Pat. 2,287,455, June 23, 1942. 



13. Lee, H. C. Process for Making Re- 
fractory Materials. U.S. Pat. 2,272,324, 
Feb. 10, 1942. 



24. Spencer, D. R. F. Developments 
in LD Refractories. Refractory J., 
November-December 1975, pp. 8-26. 



14. 
Ceram. 
pp. 807-811. 



_. Dead-Burned Dolomite. Am. 
Soc. Bull., v. 41, No. 12, 1962, 



15. Leonard, L. A. Dolomite and Sil- 
ica — Survival or Revival. The Refractory 
J., September-October 1978, pp. 12-27. 

16. Marr, R. J. High Purity Doloma as 
a Refractory Material. Pres. at ILAFA/ 
ALAFAR Conf., Lima, Peru, Nov. 2-5, 1980, 
22 pp.; available upon request from J. E. 
Baker Co. , York, PA. 



25. Szabo, M. W. Private Communica- 
tion 1980. Available upon request from 
M. W. Szabo, Ala. Geol. Survey, Univer- 
sity, AL. 

26. Weitz, J. H. High-Grade Dolomite 
Deposits in the United States. BuMines 
IC 7226, 1942, 86 pp. 

27. West Virginia Geological and Eco- 
nomic Survey. West Virginia Mineral Pro- 
ducers Directory, MRS No. 1, 7th ed. , 
1980, 110 pp. 



17. Obst, K. H. , and W. Muenchberg. 
Mineralogical Studies of Dolomite as 



*U.S. GOVERNMENT PRINTING OFFICE: 1983-605-015/03 



INT.-BU.OF MINE5,PGH.,PA. 26607 



Hl8-8^ - 



.V - 



« \/ *«£ \S •'£& V* ^- <w> -:m 



^^'• 












* "^ A *> ' 






i?v„ 



.iVA^ ** /6fek\ V.^ .-isSi^ ^** :»\%.^ .-isS^-. *«-*♦ -\ 



vv 
s v VP 



<PV 

* aV «K . 



V-C 



vv 

C, vP 






» ^ 



AT * 


















TV* 4 ,o 



•*Se. A^ 

\^ * . » * A <!\ 









/.:^:.x .^iife-v y-:tf:..v ^jas-.^ 





o *o.»» A 






A> o •> ■> „ <> 




>V 




'^/ 



• ^^ 



"'bV 






^^ >p-v 







w<v 




















>^ 



%<. 










- f++ 



„& ^ 
















^o 5 

^ 4 










^°* 









'<>. 






V J site*. \ S >:«:•- °* 








« I 1 • A 




*P^ 

l "« "*A -.CT c°" °* C> 













♦♦-♦♦ .-i^Ste V 




